If keep Priority mode on, you won't see casts like this from people you don't follow. 

Casts like this from people you don't follow make people mad.

Is this spam? How would you classify? What happens when a "good" user does this ironically?

There are bad but when these are DMs they're really bad - so filtering DMs by follow / power badge like X would be really good

I forget which but by default DMs are set to one of the two lower options (follow + recommended I think), you have to change it to everyone for every person to be able to dm. 

Might just be “recommended” people slipping through?